The invention relates to a method and an apparatus for venting a crankcase of an internal combustion engine wherein, during partial load engine operation, the crankcase is in communication with the engine intake duct downstream of a throttle valve and, during full load engine operation the crankcase is in communication with the intake duct upstream of the throttle valve.
When reciprocating-piston internal combustion engines are operating, pressure fluctuations occur in the crankcase as a result of the piston movements. The pressure of blow-by gases is superimposed on these pressure fluctuations. Blowby gases primarily comprise combustion gases which during combustion are formed at high pressure in the combustion chamber and pass via the piston ring seals into the crankcase. An excessively high pressure in the crankcase reduces the efficiency of the reciprocating-piston internal combustion engine and entails the risk of lubricating oil escaping outward via shaft seals. A pressure which is too low may cause unfiltered air from the environment to enter the crankcase, leading to increased wear caused by dirt particles. Furthermore, the acid-forming exhaust gas constituents NOx and SOx which are contained in the blow-by gases react with water to form acids. To prevent corrosion within the internal combustion engine, the acids have to be neutralized by basic additives in the oil which is present in the crankcase. During this process, the additives are consumed, leading to the ageing of the oil and the formation of a slurry, which means that relatively short oil change intervals have to be adhered to.
For the reasons which have been outlined, the reciprocating-piston internal combustion engines have an apparatus for venting the crankcase; to protect the environment from pollutants, the venting gases are introduced into the intake system. To prevent too much oil and too many dirt particles from entering the intake system, an oil separator is provided in the venting line between the crankcase and the intake system.
DE 197 09 910 C2 discloses a crankcase venting arrangement for an internal combustion engine, in which the crankcase is connected to the intake system via a venting line, which opens out into an induction pipe of the internal combustion engine downstream of a throttle valve. An oil separator and a static throttle, which limits the quantity of gas sucked out of the crankcase, is arranged in the venting line. The throttle may also be a dynamic throttle, in the form of a valve. The venting line is used to vent the crankcase in particular when the internal combustion engine is operating under part-load, when the pressure downstream of the throttle valve is relatively low. Furthermore, there is a second venting line with an oil separator which opens into the intake system upstream of the throttle valve. This second venting line is active in particular when the internal combustion engine is operating under full load when the throttle valve is approximately fully open and the pressure drop at the throttle valve is correspondingly low. If the throttle valve is increasingly closed in the part-load range, the pressure drop at the throttle valve rises, so that fresh air is drawn into the crankcase via the second venting line, with the result that the blow-by gases are purged out of the crankcase by the fresh air via the first venting line.
The blow-by gases also contain unburned hydrocarbons, which are largely completely burnt during the subsequent combustion operation and therefore do not enter the exhaust system. Unburned hydrocarbons in the blow-by gases cannot be burnt in the internal combustion engine is in an overrun or engine braking mode with an excess of air and are instead converted in catalytic converters which may be provided in the exhaust system, which represents an unnecessary burden on the catalytic converters.
US 2003/106543 discloses a crankcase venting arrangement for a turbocharged internal combustion engine. In this case, during naturally aspirated operation of the internal combustion engine, the crankcase is vented via a first venting line, which opens out into an intake line of the internal combustion engine downstream of a throttle valve. During the supercharging of the internal combustion engine by means of an exhaust gas turbocharger, the first venting line is closed by means of a non-return valve, while a second venting line connects the crankcase to the intake side of the compressor. The first and second venting lines branch off from a common venting line section. To ensure that no air is sucked in by the internal combustion engine from the induction side of the compressor via the second and first venting lines during naturally aspirated operation, the second venting line is closed by a non-return valve during naturally aspirated operation.
It is the object of the present invention to protect an exhaust gas catalytic converter of an internal combustion engine from high loading by unburned hydrocarbons.